1. Field
One or more embodiments of the present invention relate to a magnetic resonance imaging (MRI) apparatus and method, and more particularly, to an MRI apparatus and method that perform under-sampling on a plurality of pieces of K-space data acquired by a radio frequency (RF) multi-coil to acquire an MR image.
2. Description of the Related Art
A magnetic resonance imaging (MRI) apparatus is an apparatus that photographs an object by using a magnetic field. An MRI apparatus is capable of illustrating lumbar discs, joints, and nerve ligaments, in addition to bones, three-dimensionally at a desired angle. These apparatuses are therefore widely used for an accurate diagnosis of a disease.
An MRI apparatus acquires a magnetic resonance (MR) signal, reconfigures the acquired MR signal into an image, and outputs the image. Specifically, an MRI apparatus acquires the MR signal by using radio frequency (RF) coils, a permanent magnet, and a gradient coil.
Specifically, by using a pulse sequence used to generate an RF signal, an MRI apparatus applies the RF signal to an object through an RF multi-coil, and performs sampling on an MR signal generated in response to the applied RF signal to restore an MR image.
At present, about one hour is used for capturing an MR image. Generally, the MRI apparatus is implemented as a long and narrow tube (hereinafter referred to as an MRI tube). Therefore, a patient to be photographed for obtaining an MR image enters an MRI tube, and should not move while photographing. Due to this, it is difficult to capture an MR image of a critical patient or a claustrophobe, and moreover, even for general patients, a photographing time becomes longer, causing boredom and inconvenience.
Therefore, an image processing apparatus and method for shortening a capturing time of an MR image are needed.
A method, which does not perform sampling of an MR signal for all lines of a K-space image but performs under-sampling that performs sampling of the MR signal at some line intervals of the K-space image, and calibrates the under-sampled K-space data to perform imaging on a final MR image, may be used to shorten a capturing time of an MR image.
Specifically, a generalized auto-calibrating partially parallel acquisition (GRAPPA) method, which is an example of a k-space-based imaging method, performs self-calibration to calculate a spatial correlation or convolution kernel coefficient that is a spatial interaction value between a calibration signal and a measured source signal adjacent thereto, and estimates an unmeasured signal by using the calculated spatial correlation coefficient.
In detail, the GRAPPA method restores unobtained k-space lines by channel by using a measured signal that is under-sampled data and additionally acquired auto-calibration signal (ACS) line data.
In restoring k-space data by performing calibration, when data of an image signal is damaged or a spatial interaction value is changed due to noise, aliasing artifacts and amplified noise of a finally acquired MR image occur.
Therefore, it is required to provide an imaging method and apparatus that decreases the number of aliasing artifacts, and restores an MR image with an improved quality by removing amplified noise.
However, due to tradeoff, it is difficult to satisfy all the above-described requirements for reducing a time taken in capturing an MR image and for improving a quality of a restored MR image.